The invention relates to a bumper system for a motor vehicle.
The primary purpose of bumper systems is to absorb the impact when a motor vehicle strikes an obstacle, and to protect the vehicle body from structural damage during a low-speed collision. Bumper systems also protect pedestrians when they come into contact with a motor vehicle.
GB 951,690 provides a bumper system for a motor vehicle. The bumper system has an energy absorption element that extends perpendicular to the direction of travel and is connected to the vehicle frame. The energy absorption element has two parallel sub-elements that are supported on a support and on one another. These sub-elements are embodied as long shells that have a curved vertical cross-section. Both the sub-elements and the support for the sub-elements comprise plastic.
The support has projections along its upper and lower longitudinal edges. These projections oppose grooves on the adjacent inner sub-element. This sub-element itself possesses projections that face the support and that are disposed at intervals adjacent to the sides of the projections on the support that face one another. A free space is formed between the inner sub-element and the support because of the curved shape of the inner sub-element and the straight extension of the support between its projections.
Tapered upper and lower longitudinal edges of the sub-outer element that face away from the support are disposed on the convex surfaces of the inner sub-element. These convex surfaces face the outer sub-element and are also tapered at their ends. In addition, the outer sub-element has inner projections that oppose grooves on the inner sub-element.
The sub-elements and the support are held in the ready position by means of bolts. The bolts are integrally joined to the outer sub-element, pass through openings that are approximately centered in terms of height in the inner sub-element and in the support, and are secured in position by means of a transverse pin.
A free space is also provided between the outer sub-element and the inner sub-element.
If the motor vehicle comes into contact with an obstacle, the outer sub-element is displaced horizontally towards the support. The upper and lower longitudinal edges of the outer sub-element slide onto the convex sides of the inner sub-element towards its upper and lower longitudinal edges. The projections of the outer sub-element move into contact with the grooves of the inner sub-element, and the projections on the inner sub-element move into contact with the projections on the support. Because of this contact, the sides of the inner sub-element nest about the projections on the support so that these projections catch in the grooves adjacent to the projections on the inner sub-element.
The free space between the outer sub-element and the inner sub-element, and the free space between the inner sub-element and the support, are generally or largely maintained.
A prolonged impact force causes the vertical extension of the two sub-elements. The projections on the outer sub-element slide out of the grooves on the inner sub-element and over the upper and lower projection-like limits for the grooves on the inner sub-element. Since this force is transmitted onto the inner sub-element, the projections on the inner sub-element also slide over the projections on the support. Now, the free space between the outer sub-element and the inner sub-element disappears. The upper and lower sides of the outer sub-element detach again from the opposing upper and lower sides of the inner sub-element.
The stress on the vehicle frame is reduced due to the flexibility provided by the sub-elements.
The sub-elements can return to their original configuration when the force is gone.
A bumper system is known from DE 10 2005 024 094 A1. In it, a bumper cross-member has a hollow profile with at least two wings joined to one another via a bending site. In a collision, the wings pivot about the bending site with the goal of increasing the height of the bumper cross-member and reducing the depth.
An energy absorption element on the end-face of a support is known from EP 2 078 642 A1. It has two legs that are joined to one another via a predetermined breaking point. The legs are supported on the support on surfaces. When a force acts thereon, the legs slide upward and downward relatively along the support. That is, they open up and the predetermined breaking point breaks.
The energy absorption element in EP 1 564 079 A1 is provided with a profile that has a W-shaped vertical cross-section. This profile can extend vertically when an impact force acts on it.
A cross-member is known from JP 04 154 457 A. An energy absorption element made of foam is provided between it and a front cover. The cross-member is joined to crush boxes via connecting bars. When there is an impact, the energy absorption element deforms, the cross-member is displaced downward, and the connecting bars deform, as well.
In JP 03 284 442 A, an energy absorption element made of foam is fixed in a chamber that is circumferentially delimited by a sheet. When there is an impact, the energy absorption element is compressed, with the upper and lower edge sheets buckling upwardly and downwardly.